A successful `pnpm add` is no longer the end of `plugins/install`: a new
package that declares neither a bundle nor a plugin module, or a bundle
whose row id a composed layer already owns, is removed again and reported
under `removed` with its reason, while a package the probe refused stays
for the view to explain. The profile manifest is snapshotted before the run
and restored when pnpm fails. The manager refuses a second mutation while
one runs (`plugins/busy`) instead of racing on the manifest and user
layers, and `install`/`uninstall` refuse while a session is running
(`plugins/agents-running`), because pnpm rewrites the directory those
sessions import from.
`resolveProfileLayer` factors one bundle's layer out of `loadProfile` so the
manager can judge a candidate against the composed layers.
Yichen Jiang
e3386d1105